I discovered the following on my own vehicle. Have since found out that others are having the same issue. It only applies to HID lamps, not halogen (H7) lamps.
The vehicle had extremely poor output from the headlamps. The lenses were in good condition, so next port of call were the bulbs themselves. 2 very expensive HID bulbs later and very little change, so not bulbs. Ballasts/ignitors then? Unlikely to have both fail in the same way at the same time, but possible I guess. The local auto electrician had a 12v LED conversion kit for less than the price of 1 ballast, so that seemed the way to go. Output still very poor. So it turns out that the coating on the reflector has degraded and is flaking off. Lights need replacement. Choice. Brand new HID are over a grand each, second-hand are like hens teeth, and even then the ones we got were failing with the reflectors starting to flake. My next question, do we really need HID? Order a pair of second-hand halogen lamps. The old hens teeth bite again. Can get a mint right hand lamp, no lefts. Much research and a heap of phone calls later and a set of brand new halogen lamps arrive, for a price similar to second-hand too. As a bonus the plug is the same so they slot straight in. Lamps aligned and WOF issued. What a process!
So all my research showed me the myriad of lamps available for these cars. Here's the list....
HID with black inserts and auto height adjustment
HID with chrome inserts and auto height adjustment
Halogen, black, with auto adjust
Halogen, chrome, with auto adjust
Halogen, black, manual adjust
Halogen, chrome, manual adjust
Now that's just for MY09/10. I didn't get into options for MY11 to 15. We ended up with the manual adjust chromes, and I reckon they look pretty sharp. I plan on doing a LED conversion on it early next year and get some real output.